Fiber optic article with inner region

Abstract

A fiber optic article can comprise a core, an inner region disposed about the core and a cladding disposed about the inner region. The index of refraction of the cladding can be less than that of the inner region, and the index of refraction of the inner region can be less than that of the core. The fiber can include a second cladding disposed about the cladding, where the second cladding has an index of refraction that is less than the index of refraction of the cladding. The inner region can have a non circular outer perimeter that includes at least one inwardly oriented section. The article can be elongate along a longitudinal axis and can include at least one longitudinally extending region, such as a stress inducing region, for providing birefringence and the inwardly oriented region can face the longitudinally extending region. The fiber optic article can include active material for providing light responsive to the article receiving pump light, such as, for example, one or more rare earths. The rare earths can include erbium and ytterbium.

1. A fiber optic article, comprising:
 a core; 
 an inner region surrounding said core, said inner region having inner and outer perimeters spaced by a thickness T 1  therebetween, a first cross sectional area defined as all the area within said outer perimeter of said inner region; 
 a cladding surrounding said inner region, said cladding having inner and outer perimeters spaced by a thickness T 2  therebetween, said outer perimeter of said cladding having a geometric center; 
 a second cladding disposed about said cladding; 
 said inner region having an index of refraction that is less the index of refraction of said core, said cladding having an index of refraction that is less than the index of refraction of said inner region and said second cladding comprising an index of refraction that is less than the index of refraction of said cladding; and 
 wherein T 2  is greater than T 1 , said outer perimeter of said inner region is non-circular in shape, the geometric center of said cladding lies within said first cross sectional area and said T 1  refers to a maximum thickness of said inner region and said T 2  refers to a maximum thickness of said cladding. 
 
   
   
     2. The optical fiber of  claim 1  wherein said outer and inner perimeters of said inner region define a cross sectional area A 1  therebetween and said outer and inner perimeters of said cladding define a cross sectional area A 2  therebetween, and wherein A 2  is greater than A 1 . 
   
   
     3. The fiber optic article of  claim 1  wherein said outer perimeter of said inner region comprises a non-oval shape. 
   
   
     4. The fiber optic article of  claim 1  wherein said outer perimeter of said inner region comprises at least one inwardly oriented section. 
   
   
     5. The fiber optic article of  claim 1  wherein said outer perimeter of said inner region comprises at least one outwardly oriented region. 
   
   
     6. The fiber optic article of  claim 1  wherein said outer perimeter of said inner region comprises at least one substantially straight section. 
   
   
     7. The fiber optic article of  claim 1  wherein at least the majority of the length of said outer perimeter of said inner region conforms to a circle having a substantially constant radius. 
   
   
     8. The fiber optic article of  claim 1  comprising a rare earth. 
   
   
     9. The fiber optic article of  claim 1  wherein said core comprises erbium and ytterbium. 
   
   
     10. The fiber optic article of  claim 1  wherein said article comprises a fiber having an operating wavelength and wherein said core is multimode at said operating wavelength. 
   
   
     11. The fiber optic article of  claim 9  wherein said operating wavelength is greater than 500 nm. 
   
   
     12. The fiber optic article of  claim 1  wherein the numerical aperture of said core is less than 0.12. 
   
   
     13. The fiber optic article of  claim 12  wherein fiber has an operating wavelength and wherein said core is a multimode core at said operating wavelength. 
   
   
     14. The fiber optic article of  claim 1  wherein the numerical aperture of said core is less than 0.09. 
   
   
     15. The fiber optic article of  claim 14  wherein said fiber has an operating wavelength and wherein said core is multimode at said operating wavelength. 
   
   
     16. The fiber optic article of  claim 1  wherein said cladding consists essentially of fused silica. 
   
   
     17. The fiber optic article of  claim 1  wherein said article has a longitudinal axis, said fiber comprising at least one longitudinally extending region for providing birefringence. 
   
   
     18. The fiber optic article of  claim 1  wherein said fiber optic article is an optical fiber having an operating wavelength at which said fiber supports at least two modes each having an effective index of refraction that is greater the index of refraction of said inner region. 
   
   
     19. The fiber optic article of  claim 18  wherein said operating wavelength is greater than 900 nm. 
   
   
     20. The fiber optic article of  claim 18  wherein said fiber optic article includes at least one rare earth such that responsive to said article being pumped by light having a first wavelength said at least one rare earth can provide light having a second wavelength that is different than said first wavelength, and wherein said operating wavelength comprises said second wavelength.